1. Field of the Invention
The present invention relates generally to read sensors of magnetic heads in data storage devices, and more particularly to read sensors of the current-perpendicular-to-the-planes (CPP) type.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads which include read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR heads, may be used to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer. The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which the MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage. Within the general category of MR sensors is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. GMR sensors using only two layers of ferromagnetic material (e.g. nickel-iron, cobalt-iron, or nickel-iron-cobalt) separated by a layer of nonmagnetic material (e.g. copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect.
One of the ferromagnetic (FM) layers referred to as the pinned layer has its magnetization typically pinned by exchange coupling with an antiferromagnetic (AFM) layer (e.g., nickel-oxide, iron-manganese, or platinum-manganese). The pinning field generated by the AFM pinning layer should be greater than demagnetizing fields to ensure that the magnetization direction of the pinned layer remains fixed during application of external fields (e.g. fields from bits recorded on the disk). The magnetization of the other FM layer referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (the signal field). The pinned layer may be part of an antiparallel (AP) pinned structure which includes an antiparallel coupling (APC) layer formed between first and second AP pinned layers. The first AP pinned layer, for example, may be the layer that is exchange coupled to and pinned by the AFM pinning layer. By strong antiparallel coupling between the first and second AP pinned layers, the magnetic moment of the second AP pinned layer is made antiparallel to the magnetic moment of the first AP pinned layer.
Sensors are classified as a bottom sensor or a top sensor depending upon whether the pinned layer is located near the bottom of the sensor close to the first read gap layer or near the top of the sensor close to the second read gap layer. Sensors are further classified as simple pinned or AP pinned depending upon whether the pinned structure is one or more FM layers with a unidirectional magnetic moment or a pair of AP pinned layers separated by the APC layer with magnetic moments of the AP pinned layers being antiparallel. Sensors are still further classified as single or dual wherein a single sensor employs only one pinned layer and a dual sensor employs two pinned layers with the free layer structure located there between.
A read sensor may also be of a current-perpendicular-to-the-planes (CPP) type in which current flows perpendicular to the major planes of the sensor layers. First and second shield layers engage the bottom and the top, respectively, of the sensor so as to simultaneously serve as electrically conductive leads for the sensor. The CPP sensor may be contrasted with a current in parallel to the-planes (CIP) type sensor in which the current is conducted in planes parallel to the major thin film planes of the sensor. In a CPP sensor, when the spacer layer between the free layer and the AP pinned structure is nonmagnetic and electrically conductive (such as copper), the current is referred to as a “sense current”; however when the spacer layer is nonmagnetic and electrically nonconductive (such as aluminum oxide), the current is referred to as a “tunneling current”. Hereinafter, the current is referred to as a perpendicular current Ip which can be either a sense current or a tunneling current.
When the magnetic moments of the pinned and free layers are parallel with respect to one another the resistance of the sensor to the perpendicular current Ip is at a minimum, and when their magnetic moments are antiparallel the resistance of the sensor to the perpendicular current Ip is at a maximum. A change in resistance of the sensor is a function of cosine θ, where θ is the angle between the magnetic moments of the pinned and free layers. When the perpendicular current Ip is conducted through the sensor, resistance changes, due to field signals from the rotating magnetic disk, cause potential changes that are detected and processed as playback signals. The sensitivity of the sensor is quantified with a magnetoresistive coefficient Δr/R, where Δr is the change in resistance of the sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the sensor at minimum resistance.
CPP read sensors require insulator materials in the side regions to isolate the perpendicular current Ip through the read sensor structure in the central region. The insulator materials are deposited in the side regions with a sufficient thickness so as to help align subsequently deposited magnetic hard bias materials with a free layer structure in the read sensor structure. The insulator materials, however, also become formed along sidewalls of the read sensor structure. Unfortunately, the sufficient thickness of the insulator materials necessary to achieve the alignment increases a separation distance between the free layer structure and the magnetic hard bias materials. This reality decreases the effectiveness of the magnetic hard bias materials. Further, metallic seed materials are also deposited to set a texture for the successful deposition of magnetic hard bias materials. However, the metallic seed materials also become formed along the sidewalls of the read sensor structure which further increases the separation distance between the free layer structure and the magnetic hard bias materials.
Conventional processes also utilize a bilayer resist structure during milling steps for removal of read sensor materials in the side regions, in order to define a trackwidth for the CPP sensor. In the bilayer resist structure, the bottom layer is undercut with respect to the top layer of the resist. Ion milling is used to remove read sensor layers not protected by the bilayer resist. Ion beam deposition may be used to subsequently deposit insulator, magnetic hard bias and lead materials over the structure. Due to the fact that the bottom layer of the resist is undercut with respect to the top layer, the insulator, magnetic hard bias, and lead materials do not coat the sides of the bottom layer of the resist. Thus the sides of the bottom layer of the resist and the overhang of the top layer of the resist are exposed so that solvents can be used to attack the resist layers and lift-off the insulator, magnetic hard bias and lead materials that coats the dual layer resist above the read sensor structure.
Problems arise, however, when one attempts to extend bilayer resist usage to very small dimensions for CPP sensors. Specifically, the bilayer resist results in the insulator materials being deposited over top edges of the read sensor structure. This results in poor track width control, current crowding, and removal of the insulator materials over the top edges of the sensor is difficult.
Accordingly, there is an existing need to overcome these and other deficiencies of the prior art.